Apparatus for growing crystalline bodies

ABSTRACT

The apparatus comprises a gastight furnace locating a crucible which may be rotated by a motor located under the furnace. A rod vertically movable in a tubular extension of the furnace cover is adapted to pull a crystal from a melt in the crucible. The cover has a side arm which is pivotally connected to a lateral extension of a vertical shaft adapted to swing about its axis into a position where the crystal clears the furnace only after the shaft has been raised to a predetermined position. Additional pivotal movement of the side arm then provides access to the furnace body if necessary.

llited States Patent l on-at [4 1 Mar. 21, 11972 [73] Assignee:

[54] APPARATUS FOR GROWING Commissariat A LEnergie Atomique, Paris,France [22] Filed: July 22,1970

[21] Appl.No.: 57,139

3,185,551 5/1965 Djevahirdjian ..23/273 3,275,417 9/1966 Hunt ..23/273FOREIGN PATENTS OR APPLICATIONS 792,038 3/1958 GreatBritain........................23/273 Primary ExaminerNorman YudkoffAssistant ExaminerR. T. Foster Attorney-Cameron, Kerkam & SuttonABSTRACT The apparatus comprises a gastight furnace locating a cruciblewhich may be rotated by a motor located under the furnace. A rodvertically movable in a tubular extension of the furnace cover isadapted to pull a crystal from a melt in the crucible. The cover has aside arm which is pivotally connected to a lateral extension of avertical shaft adapted to swing about its axis into a position where thecrystal clears the furnace only after the shaft has been raised to apredetermined position. Additional pivotal movement of the side arm thenprovides access to the furnace body if necessary.

8 Claims, 4 Drawing Figures Patented March 21, 1972 3,650,701

5 Sheets-Sheet 1 Patented Ma rc-h 21, 1972 I v 7 3,650,701

' 5 Sheets- Sheet 2 x APPARATUS FOR GROWING CRYSTALLINE BODIESBACKGROUND OF THE INVENTION One commonly used method of growing crystalsconsists of contacting the surface of a melt with a seed crystal andthen pulling a monocrystal from the melt. Numerous systems have beendeveloped in the prior art which comprise a leaktight furnace locating acrucible. The crucible is provided with electrical resistance heatersconnected to a control device located outside the crucible formaintaining the temperature of an appropriate melt in the crucible at apredetermined value. A vertical rod slidably sealingly projects throughthe cover of the furnace and is connected to a motor which raises slowlythe rod for growing the crystal.

SUMMARY OF THE INVENTION It is an object of the invention to provide onapparatus which operates to grow a monocrystalline body from a melt andwhich comprises a furnace consisting of several parts, such apparatusbeing easier to operate and to maintain than the prior art devices.

According to the invention there is provided an apparatus for growingcrystalline bodies comprising: a leaktight furnace for containing acrystal growing melt in a crystal growing environment, said furnacehaving a tubular body and a cover in which means are vertically movablefor pulling a crystalline body from said melt, and support means whichincludes a side arm secured to said cover and pivotally connected to alateral extension of a vertical shaft vertically movable between a lowerposition and an upper position, said shaft being restrained againstrotation from an angular position where said cover is aligned with saidbody by means which are inoperative when said shaft is in an upperposition.

The invention will be better understood from a consideration of thefollowing description of an embodiment of the invention given by way ofnon-limitative example.

The description refers to the accompanying drawings wherein:

FIG. 1 schematically illustrates the apparatus in partial sectron;

FIG. 2 is an enlarged schematic fragmentary view of the shaft andofthejack assembly of the apparatus of FIG. 1;

FIG. 3 is a fragmentary section along line III-III of FIG. 1 with thecover fully offset laterally;

FIG. 4 is a fragmentary elevation of the seed pulling mechanism, on anenlarged scale and in partial section.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a closed furnaceconsisting of a generally cylindrical body 10, a lower plate 12 and adomical cover 14. The body 10 is double walled and cooling water iscirculated in the annular space between the walls during operation.rings (not shown) are located between the mating surfaces of the body10, lower plate 12 and cover 14 for retaining an appropriate atmospherewithin the furnace. The furnace cover is formed with a tubular extension18 which provides room for vertical movement of a crystal pulling rod20. A telescope 22 projecting through the cover is equipped with acalibrated graduated scale which makes it possible to measure thediameter of the crystal as it is being grown from the melt. A loophole24 closed by a quartz window (not shown) permits to monitor the crystalgrowth. The lower plate 12 of the crucible is carried by a supportbracket 26 securely connected to a vertical frame 28 of channeled crosssection (FIG. 3). The frame 28 is carried by a base plate 30 whichsupports the whole apparatus.

The crucible 16 containing the melt 34 is supported on a rod 32 which isvertically movable through an opening in the lower plate 12. The melt 34is heated by electrical resistors 36 surrounding the crucible l6 andwhose terminals 38 project out of the lower plate for connection with acontrol apparatus associated with suitable temperature sensors (notshown).

A plenum chamber 40 is formed under the lower plate 12 for receiving theatmosphere to be maintained in the furnace.

Chamber 40 is limited by the lower plate 12, a ring 42 having a gasinlet 44 and a sealing assembly 46. Stationary O-ring seals 47 arelocated between the mating surfaces of the ring 42, lower plate 12 andsealing assembly 46. A pair of lip seals 48 carried by the two walls ofassembly 46 provide a sliding fluidtight connection between the assembly46 and the rod 32 which projects out of the assembly. In the embodimentillustrated in FIG. 1, the assembly 52 includes a water box providedwith an inlet and an outlet for cooling water.

The rod is secured to the shaft of a low-speed rotary motor 50 whichrests on a vertically movable support 52: as a result, the crucible l6and rod 32 are carried by the support 52 and vertical movement of thelatter permits to adjust the height of the crucible and the level of themelt in the furnace.

The mechanism for raising and loweringthe support 52 comprises avertical column 54 mounted between the base plate 30 and bracket 26 bysuitable means such as screws or bolts. A rotatable axial screw (notshown) retained against axial movement in the column 54 may be rotatedeither by a low-speed motor 56 or by a high-speed motor 58. The support52 is provided with a sleeve which carries rollers 60 received in anaxial groove 62 of the column, thereby providing a splined connection,and with a rotatable nut threaded on the screw: as a consequence,rotation of either motor results in upward or downward movement ofsupport 52 and crucible 16.

The cover 14 and extension 18 may be lifted and rotated by an assemblywhich also supports the seed pulling mechanism, as will appear later.The extension is formed with a radial flange 64 secured to a side arm66. The side arm 66 is pivotally connected by a vertical pin 68 in alateral extension 70 of a vertical shaft 72 (FIG. 1 and 3). A releasablelatch 71 normally retains the extension 70 and side arm 66 in alignment.The shaft 72 is guided by bearings 74 secured to the frame 28 and keys76 carried by the shaft are slidably engaged in keyways 78 of thebearing and retain the shaft 72 against rotation except when the shaftis in the vertical position illustrated in FIG. 2. Vertical movement ofthe shaft 72 is controlled by an electric jack whose cylinder 80 isconnected to a bracket 82 of the frame by a pin 84 and whose piston rod86 is pivotally connected to the shaft.

As shown on FIG. 1 -2, the shaft is free to rotate only after is hasbeen raised from the position which corresponds to closed condition ofthe furnace by an amount sufficient for the lower key 76 to clear thecorresponding keyway 78 (FIG. 2), but smaller than that which wouldcorrespond to engagement of the upper key 76 with the correspondingbeyway. Angular movement of the shaft when in the location of FIG. 2 ishowever restrained by the size of openings 77 inthe stationary frame 28to a predetermined angle a (FIG. 3). The angle a is so selected as tocorrespond to a location of the cover for which the seed pullingmechanism is laterally displaced beyond the body of the crucible, makingit possible to withdraw the crystal by separating it from the mechanismand removing it downwardly.

The components of the seed pulling mechanism (FIG. 1 and 4) are similarto those of the mechanism for rotating the crucible and moving itvertically. The seed pulling rod 20 has a terminal chuck (not shown) andprojects through a water-cooled sealing assembly provided with lip seals48'. The rod is supported by a rotating motor 50 carried by a support52. The support 52 is adapted to be raised and lowered by a screw andnut connection actuated either by a high-speed motor 58' or by alow-speed motor 56' carried by a transverse arm 88 of the shaft 72. Thescrew 92 is retained against axial movement in column 54' by bearings 94while the nut 96 is connected by a pin 98 to a sleeve integral withslide arm 52' and slidably nonrotatably engaging the sides of alongitudinal slit I00 of the column. Metal bellows 102 provide aflexible gastight connection between the upper opening of the tubularextension 18 and the sealing assembly.

In order to grow a crystalline body, the crucible 16 is charged with anappropriate melt while the furnace is in the open condition illustratedin FIG. 3. The furnace is then closed. For this purpose, the cover 14and the tubular extension 18 are rotated about pin 68 until the side arm66 and lateral extension 70 are in aligned condition. The latch 71 isinserted and locks the side arm 66 and lateral extension in alignedrelationship. The shaft 72 is rotated in turn to the angular position ofFIG. 2 for which the cover 14 confronts the body 10. The liftingjack isdeactivated and the shaft 72 moves down along with cover 14. During thatmovement, the lower key 78 engages the corresponding keyway 76 therebyguiding the cover into accurate engagement with the upper surface of thebody. Fast action fasteners 104 are then locked manually to retain thecover.

The furnace is purged and an appropriate atmosphere is admitted into thefurnace through inlet 44. Such inert gases as nitrogen, argon and heliumare generally used although in certain cases a chemically reducingatmosphere or a vacuum may be preferable. The electrical resistanceheater 36 is then energized until the charge in crucible 16 is meltedand a suitable temperature is attained.

From this point on the sequence of operation is conventional. It mayhowever be noted that during the crystal growing operation the melt 34is continuously rotated by motor 50 and the interface is maintained at asubstantially constant level using the low-speed motor 56. The rod 20 isalso rotated by motor 50 and slowly lifted by the low-speed motor 56'which permit to adjust the speed of growth of the crystal; on thecontrary the high-speed motors 58 and 58' are used for movement of thecrucible and rod prior to initiation of the crystal pulling Step.

When a crystal body of sufficient length has been pulled, contact isbroken between the body and melt by an increase of the speed of pull fora short time duration. The pulling mechanism is deactivated until thecrystal has cooled down. Access may be gained to the crystal for removalthereof by energization of the jack 80 for lifting the shaft 72 from theposition of FIG. 1 to the position of FIG. 2. The cover crystal pullingmechanism and shaft 72 are then rotated about the shaft axis by an angle(1 thereby bringing the crystal to a position making it possible toremove it downwardly without interference with the body of the furnace.Care is of course to be taken to avoid that the lower end of the crystalprojects down to a level below that ofthe upper surface of body 10. Ifin addition the crucible and/or the inner surface of the furnace are tobe cleaned, access may be had to them after the cover has been rotatedabout pin 78 by an additional angle B (FIG. 3). This may be done afterthe latch 71 has been removed.

Although a single embodiment of the invention has been illustrated anddescribed in full detail, it will be apparent to those skilled in theart that numerous modifications are possible. It should be understoodthat the invention is not limited to the preceding description, but onlyby the appended claims.

We claim:

1. An apparatus for growing crystalline bodies comprising:

a leaktight furnace for containing a crystal growing melt in acrystal/environment, said furnace having a tubular body and a cover,

means vertically movable in said cover for pulling a crystalline bodyfrom said melt,

and support means for said cover, said support means including:

a side arm secured to said cover,

a vertical shaft having a lateral extension pivotally connected to saidside arm, and vertically movable,

and means for preventing said shaft from rotating from an angularposition where said cover is vertically aligned with said body, saidmeans being inoperative when said shaft is at a predetermined level forwhich said cover is out of engagement with said body.

2. An apparatus according to claim 1, including means for limiting theextent of pivotal movement of said shaft when in said predeterminedposition.

3. An apparatus according to claim 2, wherein the extent of angularmovement of said shaft is just sufficient for the crystal pullingmechanism to clear the body laterally.

4. An apparatus according to claim 2, having manually releasable lockingmeans for retaining said lateral extension and side arm in alignedcondition.

5. An apparatus according to claim 4, having means for restrainingpivotal movement of said side arm to an extentjust sufficient for thecover to clear said body upon combined pivotal movement of said sode armand shaft.

6. An apparatus according to claim 1, including a splined connectionbetween said shaft and a stationary frame, said connection beinginoperative when said shaft is at said predetermined level.

7. An apparatus according to claim 1, wherein said shaft carries saidcrystal pulling means.

8. An apparatus according to claim 1, having a crucible in said furnace,a vertical rod slidably sealingly projecting through a bottom assemblyof said furnace, motor means for rotating said rod and crucible, andmotor means for moving said rotating means, rod and crucible verticallyas a whole.

2. An apparatus according to claim 1, including means for limiting theextent of pivotal movement of said shaft when in said predeterminedposition.
 3. An apparatus according to claim 2, wherein the extent ofangular movement of said shaft is just sufficient for the crystalpulling mechanism to clear the body laterally.
 4. An apparatus accordingto claim 2, having manually releasable locking means for retaining saidlateral extension and side arm in aligned condition.
 5. An apparatusaccording to claim 4, having means for restraining pivotal movement ofsaid side arm to an extent just sufficient for the cover to clear saidbody upon combined pivotal movement of said sode arm and shaft.
 6. Anapparatus according to claim 1, including a splined connection betweensaid shaft and a stationary frame, said connection being inoperativewhen said shaft is at said predetermined level.
 7. An apparatusaccording to claim 1, wherein said shaft carries said crystal pullingmeans.
 8. An apparatus according to claim 1, having a crucible in saidfurnace, a vertical rod slidably sealingly projecting through a bottomassembly of said furnace, motor means for rotating said rod andcrucible, and motor means for moving said rotating means, rod andcrucible vertically as a whole.